1. Field of the Invention
The present invention relates to a head suspension having a piezoelectric element that deforms in response to a voltage applied thereto and is fitted through at least an electric insulating layer to a fitting part of a base of the head suspension.
2. Description of Related Art
Small-sized, precision information devices are rapidly advancing and needs for micro-actuators capable of conducting positioning control for very small distances in such devices are also increasing. The devices that particularly need such micro-actuators include optical systems for correcting focuses and inclination angles, ink jet printers for controlling ink heads, and magnetic disk drives for controlling magnetic heads.
The magnetic disk drives have an urgent issue to solve, i.e., increasing storage capacity. The storage capacity of a magnetic disk drive will increase if the storage capacity of each magnetic disk in the magnetic disk drive increases. The storage capacity or recording density of the magnetic disk will increase, without changing the diameter thereof, if the number of tracks per inch (TPI) on the magnetic disk increases. For this, the width of each track on the magnetic disk must be narrowed. To handle such narrow tracks on a magnetic disk, a magnetic head of a head suspension in the magnetic disk drive must conduct precise positioning in a direction across the tracks. For realizing the precise positioning, there is a need of an actuator capable of accurately moving and positioning the magnetic head of the head suspension within a very small area.
To meet the need, the applicant of the present invention has proposed in Japanese Unexamined Patent Application Publication No. 2002-50140 a head suspension for a disk drive. The head suspension includes a base plate, a connection plate having a hinge thinner than the base plate, a load beam provided with a flexure and a magnetic head, and a pair of piezoelectric elements.
This related art employs a dual actuator system for positioning the magnetic head. The dual actuator system involves a voice coil motor and the piezoelectric elements made of PZT (lead zirconate titanate).
The piezoelectric elements minutely drive a front end of the load beam in a widthwise direction (sway direction) of the head suspension. Compared with a single actuator system employing only the voice coil motor, the dual actuator system employing the voice coil motor and piezoelectric elements more precisely positions the magnetic head attached to the front end of the head suspension.
An important issue for the head suspension employing the dual actuator system is how to mount the piezoelectric elements on the head suspension.
As an approach to address the issue, the applicant of the present invention has proposed in Japanese Unexamined Patent Application Publication No. 2002-184140 (in particular, an adhesive layer 80 in paragraphs 0024 to 0026 and FIG. 5) a head suspension for a disk drive. The head suspension includes a load beam, a flexure attached to the load beam, an actuator base including a base plate, and a pair of piezoelectric elements. The actuator base has an attaching part to which the pair of piezoelectric elements is attached through the adhesive layer that is electrically insulative.
The adhesive layer according to this related art includes an adhesive that functions as an electrically insulative matrix resin and a granular filler. The granular filler is made of an electrically insulative material and is mixed with the adhesive. The granular filler interposes between the piezoelectric elements and the attaching part, to secure electric insulation.
According to this related art, there will be a situation that there is little or no granular filler in the adhesive between the piezoelectric elements and the attaching part. To avoid such a situation, a relatively wide space including a designing allowance must be maintained between the piezoelectric elements and the attaching part. This results in increasing the size of the attaching part and leaving a miniaturization request for head suspensions unfulfilled.